With the Voodoo Child release, the syntax to invoke a scan changes

[vocatan]

the verb from 'scan' to malware-scan

Installation.md needed to be updated to reflect this.

The Docker instruction:

$ docker run -v /var/www:/var/www wordfence-cli:latest scan --version
The "scan" subcommand has been renamed to "malware-scan"
$ docker run -v /var/www:/var/www wordfence-cli:latest malware-scan \
--version
Wordfence CLI 2.0.2 "Voodoo Child"
PCRE Version: 8.39 2016-06-14 - JIT Supported: Yes

The native invocation:

$ python main.py scan --version
The "scan" subcommand has been renamed to "malware-scan"
$ python main.py malware-scan --version

             ▓▓▓
        ▓▓▓▓▓   ▓▓▓▓▓          _       __               __  ____
  ▓▓▓▓▓▓▓           ▓▓▓▓▓▓▓   | |     / /___  _________/ / / __/__  ____  ________
 ▓▓           ▓           ▓▓  | | /| / / __ \/ ___/ __  /_/ /_/ _ \/ __ \/ ___/ _ \
▓▓     ▓▓    ▓▓▓    ▓▓     ▓▓ | |/ |/ / /_/ / /  / /_/ /_  __/  __/ / / / /__/  __/
▓▓      ▓     ▓     ▓      ▓▓ |__/|__/\____/_/   \____/ /_/  \___/_/ /_/\___/\___/
▓▓    ▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓    ▓▓                                       ____ _     ___
▓▓  ▓▓▓ ▓    ▓▓▓    ▓ ▓▓▓  ▓▓                                      / ___| |   |_ _|
▓▓▓▓▓   ▓    ▓▓▓    ▓   ▓▓▓▓▓                                     | |   | |    | |
 ▓▓     ▓   ▓▓ ▓▓   ▓     ▓▓                                      | |___| |___ | |
  ▓▓▓▓▓▓▓▓▓▓▓▓ ▓▓▓▓▓▓▓▓▓▓▓▓                                        \____|_____|___|

Wordfence CLI 2.0.2 "Voodoo Child"
PCRE Version: 8.40 2017-01-11 - JIT Supported: No